The present invention relates to a method, and more particularly to a method of producing a badminton racket frame.
There are two main processes which are widely used for making or producing tennis or badminton rackets in the world today. First of all, a comparison of the playing function and the racket property between a tennis racket and a badminton racket is listed in Table 1.
TABLE 1 ______________________________________ ITEM PLAYING FUNCTION RACKET PROPERTY ______________________________________ Bad- 1 Less momentum Vibration is careless min- 2 Ball travels at a Top frame should be ton lower speed when strong and rigid, the racket striking string tension should be as high as possible 3 Power comes Flexible and explosive mostly from the powerful shaft is player himself needed 4 Big deflection at Shaft should be durable the shaft during with stiffness equal on the play its both sides Tennis 1 More momentum Vibration is crucial Racket 2 Ball travels at a Strong frame and proper higher speed when flexibility on the yoke striking area could have a good rebound and com- fortable feeling 3 Power comes Comfortable condition mostly from the area essential, for response of instant: larger sweet- stroke spot, proper weight and balance for individual players ______________________________________
It is very important that different rackets which have different function requirements should be made by different manufacturing processes.
The first method employs a foamable material. The racket comprises a core which includes a foamable material or a foamable resin composition. U.S. Pat. No. 4,129,634 to Cecka et al. discloses a method for producing a racket frame which has a strip shaped foamable plastic core disposed therein. The strip of foamable material is maintained within a seamless sleeve made of a thin, flexible cellulosic film which is disposed in an outer shell forming the racket frame. The outer shell is disposed in a mold cavity. The foamable material is caused to expand and to generate pressure within the mold cavity and thereby provide intimate bonding of the core to the shell. It is very important that a steady and firm pressure is required to be applied to the frame during the curing stage. As shown in FIG. 4, the powder of foaming agent is blended into or added to the plastics carrier in order to form a strip of foamable material. Generally, the powder of foaming agent can not be blended evenly in the plastics carrier so that the strip of foamable material has a limited uniformity and may not be expanded or inflated uniformly or evenly. In addition, the racket frame which is made by the above-mentioned method with a core disposed therein has a weight heavier than the hollow racket frames.
The second method is an air injection method which employs a pressurized air injected into the racket frame. This is the most popular method used today to manufacture both badminton racket and tennis racket. As shown in FIG. 5, the composite structure of the tennis racket frame 20 includes a plurality of layers, each made of a sheet of composite fibers, unidirectionally oriented and resin-impregnated. The tennis racket frame 20 has a fluent and smooth passage 21 or hollow interior formed therein and has no sharp angles formed therein so that the pressurized air can be easily injected into the passage 21 of the racket frame 20 from one end of the passage 21. Therefore, the air injection method is suitable for manufacturing tennis racket frames.
As shown in FIG. 6, the composite structure of the badminton racket frame comprises a shell 10 including a plurality of layers, each made of a sheet of composite fibers, unidirectionally oriented and resin-impregnated. The shell 10 includes a head section 11 and a handle shaft 12 with a passage 14 formed therethrough. One end 15 of the shell 10 is closed. A sharp angle exists between the head section 11 and the handle shaft 12 or in the so called T-joint area. During a heating process and/or a compression process, a pressurized air is continuously injected into the passage 14 from the free end of the handle shaft 12 in order to expand the shell 10 which is arranged within a mold cavity. Occasionally, the pressurized air is jammed or obstructed in the sharp angle portion of the T-joint area, and may not flow through this portion swiftly. In addition, when the pressurized air is injected into the passage 14, the head section 11 inflates and the closed end 15 has a tendency to extend toward and to press the passage 14 of the shell 10, particularly the sharp angle area so that the angle area will further be obstructed. Therefore, because of the two deadly problems as mentioned above, about 25% of the products made by this method are rejected products and are unacceptable. Furthermore, a compressor or the like is required to produce and to provide the pressurized air.
The present invention has arisen to solve the afore-described disadvantages of the conventional method for producing badminton racket frames.